1. Field of the Invention
The invention relates to gettering devices and somewhat more particularly to a controllable hydrogen source having a gettering effect for use in electronic tubes using hydrogen as a supporting gas and having a heating means therein.
2. Prior Art
In order to function, certain high vacuum electron beam tubes must be filled with a supporting gas at pressures in order of 10.sup.-3 Torr. Generally, such gas charge functions to generate ions via the electron beam. A particular example of this type of tube is a vidicon tube having a highly insulated pyroelectric image plate and operating with a stabilized cathode potential.
In such tubes, it is preferable to use hydrogen as a supporting gas since with hydrogen the damage done to an oxide cathode by ion bombardment is minimal.
In order to maintain a static high vacuum condition in an electronic tube, a getter is generally required to consume or at least bind any residual gases therein, mostly released by the electron beam during tube operation. In order to achieve such gettering in tubes working on hydrogen, only getters which do not absorb or bind hydrogen during tube operation can be utilized.
In order to optimize the relationship between electron beam density and ion density within an electron tube, the hydrogen pressure therein should be variable within certain limits. Certain metals, such as zirconium or tantalum for example, are useful in achieving the foregoing requirements. Typically, a zirconium or tantalum body is highly charged with hydrogen and positioned within the tube as a heatable plate or the like. During tube operation, such plate warms up and releases a quantity of hydrogen as a function of the plate temperature. On cooling, the released hydrogen is re-absorbed by such plate. However, such metal getter elements do not bind other residual gas that may be present in electronic tubes at relative high temperatures. Accordingly, in such cases it is necessary to provide getters which are selective for such residual gases but which do not consume or bind hydrogen. This necessity creates considerable technological problems and the invention provides method and means of substantial avoiding such problems and attendant prior art disadvantages.